In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Superabrasives, such as diamond, cubic boron nitride (“cBN”) and polycrystalline diamond (“PCD”), have been widely used in cutting elements, such as the cutting elements in drilling, mining, and woodworking applications. In one particular application, superabrasives are incorporated into drill bits for use in rock drilling and other operations which require high abrasion resistance or wear resistance. For example, U.S. Pat. Nos. 4,109,737 and 5,374,854, the disclosures of each of which are herein incorporated by reference in their entirety, describe drill bits with a tungsten carbide substrate having a polycrystalline diamond compact on the outer surface of the cutting element.
As a cutting element, the superabrasive material forms a compact, which is a mass of diamond particles or cBN particles, bonded together to form an integral, tough, high-strength mass. Diamond or cBN particles may be bonded together as a compact in a particle-to-particle self-bonded relationship, optionally with a bonding medium disposed between the particles, such as a catalyzing material used to bond the abrasive particles together. For example, U.S. Pat. Nos. 3,236,615; 3,141,746; and 3,233,988, the disclosures of each of which are herein incorporated by reference in their entirety, describe compacts and methods of forming the same.
Although formed in a near net-shape form, cutting elements have many applications when cut to shape. Currently, electrical discharge machine (“EDM”) techniques are commonly used to ablate or cut PCD or PCBN layers supported on sintered carbide substrates. It ablates using the intense heat of a hot spark. EDM cutting has a high precision, <0.008 inch kerf and results in clean cut edges. In EDM, the moving wire and water flushing effectively adheres to and then pulls away from the cut, the ablated cut material. Flushing keeps the edge cool minimizing thermal damage. However, EDM is a slow process, with cutting rates of about 5 mm2/min through PCD and carbide, and is sensitive to the electrical conductivity, and spatial variation of electrical conductivity, of PCD and PCBN, which is not well controlled in synthesis. EDM is, in practice, useless for non-conducting materials like ceramics. EDM produces miles of spent wire which must be disposed.
Another technique used to ablate or cut PCD or PCBN is laser cutting. This technique is currently gaining popularity due to very high cut rates, >250 mm2/min, potentially narrow kerf width, no consumables, high precision and reasonable cut edge quality for unsupported PCD and unsupported PCBN, where unsupported indicates there is no underlying substrate of hard material, such as cemented carbide.
A major issue with laser ablation cutting of supported PCD and supported PCBN is the recondensing or recasting of metal from the carbide support and PCD back into the kerf or along the cutting edge after the laser has passed. In laser cutting, gas is directed to the cutting area, but this is ineffective in removing the condensable metal vapor. When cutting supported PCD or supported PCBN, the metal content of carbide, conventionally approximately 6-13 wt-% cobalt, results in considerable condensable metal fume being produced. PCD contains about 5 to about 20% w/w Co metal, but since the carbide support is 10 times heavier than the PCD, the majority of metal vapor derives from the carbide support. The presence of metal fume or vapor in the cut necessitates the use of an excessively wide kerf combined with grit-blasting of the cut parts after laser cutting to keep the cut open and blast off recast metal is a large labor cost and currently consumes the time benefits of laser cutting techniques as compared to EDM techniques. The grit blasted laser cut PCD material, now free of condensed cobalt metal, is obviously rougher and potentially chipped. This method cannot be used for polished PCD as the polish will be impaired.
Furthermore the condensed metal fume puts heat of vaporization of cobalt back into the PCD. This heat can oxidize and/or crack the PCD. If laser ablation is conducted in air the metal vapor can oxidize, producing even more heat which inevitably gets into the PCD material. To prevent burning and overheating the cut edge, laser cutting of supported PCD is frequently done in nitrogen gas. This does nothing to address the heat of vaporization. Eliminating the metal from the carbide, and perhaps the PCD, eliminates all this heat and produces a less defective cut part.